In various semiconductor manufacturing processes it may be difficult to control the concentration of mobile contaminants such as ionic contaminants introduced into the wafer during manufacture. These contaminants, which are typically in the form of metal impurities, may adversely affect the electrical characteristics of the completed semiconductor devices. In order to remove these impurities, a trapping phenomenon known as gettering may be used to attract the impurities away from the semiconductor devices into inactive regions of the wafer.
As an example, U.S. Pat. No. 3,783,119 to Gregor et al. discloses a process wherein a layer of phosphorus pentoxide (P.sub.2 O.sub.5) is deposited on a layer of silicon dioxide to form a glass to getter sodium ionic impurities away from the silicon dioxide.
A gettering agent such as phosphorus may also be used to introduce interfacial misfit dislocations in the semiconductor crystal lattice. These dislocations function as a trap for the mobile ionic contaminants. This type of gettering process is usually carried out by diffusion of phosphorus into the wafer at relatively high temperatures. U.S. Pat. No. 3,997,368 to Petroff et al. discloses such a gettering process.
It is also known in the art to induce crystal damage in the semiconductor lattice by damaging the backside of the wafer. Backside damage causes the growth of dislocations that radiate up into the wafer. There dislocations then act as a gettering center or trap for the mobile impurities.
As an example the use of backside ion implantation as well as MeV Carbon implantation for gettering metal impurities has been demonstrated recently. [1] Implantation damage and phosphorus diffusion are instrumental in gettering because of the affinity of metal atoms to diffuse to inactive regions during a subsequent annealing step known as segregation annealing. Any high temperature steps after the segregation annealing however, can diminish the effectiveness of segregation by detrapping of the captured impurities.
There is therefore a need in the art for a gettering process that can be accomplished preferably subsequently to other high temperature process steps. It is therefore an object of this invention to provide a gettering process that can be consistently duplicated in large scale repetitive semiconductor manufacture subsequent to high temperature processes. It is another object of this invention to provide a gettering process that thins the wafer such that contaminants have a smaller distance to travel to gettering centers. Yet another object of the invention is to provide a gettering process using backside stress induced damage combined with diffusion of a gettering agent such as phosphorus. It is a further object of the invention to provide a gettering process that is simple, consistent, and cost effective.